The present invention relates generally to metal contact layers for integrated circuit chips, and more particularly to such metal contact layers which are devoid of opens and direct shorts to semiconductor.
The deposition of conductive material over a topography which includes an abrupt vertical step frequently results in opens or shorts through to the underlying semiconductor. Such opens or shorts cause significant declines in chip yield. Unfortunately, such vertical steps are common throughout most chips due to the need to etch through insulator layers overlying chip devices to make electrical contact thereto. Such problems are particularly severe where the sidewalls of the abrupt steps overhang a portion of the bottoms of the steps. Attempts have been made to avoid these opens and shorts by using tantalum or tungsten silicides as the wiring layer. However, such silicides have too much electrical resistance, resulting in significant heat generation. Accordingly, tantalum or tungsten silicide wiring is unacceptable for dense bipolar chip applications.
Other approaches to this problem have centered around using wide metal bands and a series of intermediate steps in place of one abrupt step. However, these approaches use a significant amount of chip real estate, thereby limiting chip device and circuit density.
The invention as claimed provides a structure and a method for eliminating shorts and opens in the contacts made through one or more insulator layers to electrical devices and circuit elements therebelow.